1. Field of the Invention
The present invention relates to trifunctional agents useful as irreversible inhibitors of A.sub.1 -Adenosine receptors.
2. Description of Related Art
Adenosine acts as a neuromodulator at two receptor subtypes: A.sub.1 - and A.sub.2 -, which in general, inhibit or stimulate adenylate cyclase, respectively. Selective agonists and antagonists of each receptor subtype have been reported. The high affinity, A.sub.1 selective antagonist 8-[4-[[[[(2-aminoethyl)-amino]carbonyl]methyl]oxy]phenyl]-1,3-dipropylxant hine (1), XAC, which has a K.sub.i value at rat brain A.sub.1 -receptors of 1.2 nM, was developed using a functionalized congener approach. Jacobson, K. A. et al, J. Med. Chem., 1985, 28:1334-40. ##STR3## XAC has been useful in characterizing the A.sub.1 receptor both as radioligand and as a ligand immobilized via its alkyl amino group for affinity chromatography of the receptor protein. Jacobson, K. A. et al, Proc. Natl. Acad. Sci. USA, 1986, 83:4089-93; Nakata, H. (1989) J. Biol. Chem., 264, 16545-16551. The m- and p-phenylenediisothiocyanate conjugates of XAC (m-DITC-XAC (2a) and p-DITC-XAC (2b))), were prepared as high affinity, irreversible A.sub.1 antagonists, with K.sub.i values at rat brain A.sub.1 -receptors of 2.4 and 6.6 nM, respectively. ##STR4## These chemically reactive ligands have been used for identifying the A.sub.1 receptor on electrophoretic gels and for blocking A.sub.1 -receptor mediated effects in physiological studies.
A general approach to systematically modifying the structure of irreversible ligand derivatives was desired to provide analogs. In previous studies of reversible ligands bearing spectroscopic labels, only moderate receptor affinities were attained, and this limited the utility of the ligands for histochemical studies. Jacobson, K. A. et al, Biochem. Pharmacol., 10:1697-1707 (1987). A spectroscopic probe that binds irreversibly to the receptor would preclude problems of rapid washout and long equilibration times associated with reversible ligands. In addition, a difficulty encountered with 8-phenylxanthine derivatives in physiological studies is their typically low water solubility. Boykin, Dennis D. et al, FASEB J., 4:A1008, Abstract 4306.